🐛 Debugging Loops — Find and Fix Problems

Every programmer encounters loop bugs. Learn to identify and fix them quickly.

🎯 Problem 1: Infinite Loops

The Problem: Loop never stops

# ❌ WRONG - count never changes
count = 0
while count < 5:
    print(count)
    # Missing: count = count + 1

The Fix:

# ✅ CORRECT
count = 0
while count < 5:
    print(count)
    count = count + 1

💡 Problem 2: Off-by-One Errors

The Problem: Loop runs one time too many or too few

# ❌ WRONG - prints 0 to 4 (wanted 1 to 5)
for i in range(5):
    print(i)

# ✅ CORRECT
for i in range(1, 6):
    print(i)

🔍 Problem 3: Loop Never Runs

The Problem: Loop condition is always False

# ❌ WRONG - condition is always False
i = 10
while i < 5:
    print(i)

# ✅ CORRECT
i = 0
while i < 5:
    print(i)
    i = i + 1

🎨 Problem 4: Indentation Errors

The Problem: Code outside loop when it should be inside

# ❌ WRONG - print is outside loop
for i in range(3):
    x = i * 2
print(x)  # Only prints once, at the end

# ✅ CORRECT - print inside loop
for i in range(3):
    x = i * 2
    print(x)  # Prints for each iteration

📊 Debugging Techniques

Technique 1: Add print statements

for i in range(3):
    print(f"DEBUG: i = {i}")  # Track variable
    # Your code here

Technique 2: Check boundary conditions

# Test with edge cases
# Empty list, single item, large numbers

Technique 3: Use a simple test case

# Don't test with 1000 items first!
# Test with 3-5 items

🔑 Key Takeaways

🔗 What's Next?

Master Best Practices for writing clean loops!

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